1. Field of the Invention
The present invention relates to an acoustic diaphragm and a method of manufacturing the same.
2. Description of Related Art
Various materials of acoustic diaphragms and methods of processing the surface of diaphragm base member have been proposed heretofore, particularly for loudspeakers for high and middle frequency use. Among such methods, as a method of forming a diamond film with less amorphism on the surface of a diaphragm base member, there are known a thermal filament method, electron impact CVD (EACVD) method, a microwave CVD (MCVD) method, a plasma jet method, a DC plasma method and the like.
There is also known a method of forming a diaphragm made of only a diamond film as disclosed Japanese Patent Laid-Open Gazette No. 61-128700. According to this method, a diamond film is deposited on a monocrystal silicon formed in the shape of diaphragm by an MCVD method using a 2.45 GHz microwave while emitting a plasma of a mixture gas composed of methane (CH.sub.4) and hydrogen (H.sub.2) and thereafter the monocrystal silicon is dissolved to obtain a diamond diaphragm.
Conventional acoustic diaphragms and manufacturing methods are associated with the following problems.
First, with the thermal filament and EACVD methods, the area of a deposited film is small, the distance to a diaphragm base material on which a film is deposited is short, and the distribution of film thickness is poor. Also as to the MCVD method, it is known that the deposition area is determined by the dimension of a silica glass tube reacting with a waveguide and the dimension of a plasma. With any one of the above conventional methods, the diameter of a deposition area is only 3 to 10 cm so that the manufacturing capability is limited about one to five diaphragms having a diameter of one inch. Further, the film deposition thickness per hour is 1 to 10 microns/cm.sup.2, resulting in high cost and poor mass productivity.
Second, since the above conventional methods form a diamond film through heating a filament, DC discharge, high frequency microwave discharge, a diaphragm base material is heated up to about 1000 degrees centigrade, resulting in deformation or damage of the base material. Thus, it is necessary to realize improved heat dissipation.
Third, with the method of manufacturing a diaphragm made of only a diamond film as disclosed in the above-described Japanese Patent Laid-Open Gazette No 61-128700, it is difficult to form a monocrystal silicon having a desired shape. The diameter of a deposited area is only 3 to 10 cm. In addition, since the deposition film thickness per hour is equal to or smaller than 1 micron/cm.sup.2, it takes several tens hours to manufacture a diaphragm having a diamond film thickness of several tens microns, leaving a problem of mass productivity.